Cummins X-15 Efficiency: HOW LOW CAN YOU (IT) GO?

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Jax Graddy, Feb 23, 2021 at 8:33 AM.

  1. Jax Graddy

    Jax Graddy Bobtail Member

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    Hey drivers!

    I'm looking at making a new truck purchase in the next 6 months. So, I'm finding out all I can about drivetrain options. Right now I'm specifically interested in the X-15 Efficiency. Not that I might not change my mind later. What I'm considering is I want a drivetrain that will be as valuable as possible when it comes time to sell it used. That's why I'm dead-set on an 18-speed. It is versatile, it is robust, it is efficient. Personally when I was looking at used trucks, I wouldn't consider anything but a 13 or 18 speed.

    Anywho - I'm interested in making a downsped truck, but with an 18 speed. At least making a downsped truck to a limited degree.

    What I would want to know is ... at how low of an RPM will the X-15 Efficiency run on the flat / level and still pull effectively / comfortably to keep it going down the road and at least pulling bunny hills?
     
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  3. Dave_in_AZ

    Dave_in_AZ Road Train Member

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    Bean Jr., baha and Dave1837 Thank this.
  4. Jax Graddy

    Jax Graddy Bobtail Member

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    Is that the thread that the 12 year old kid got on there and wreaked havoc (for a while)? If so, I read the whole thread. I'll check it either way. If it's not the same, I'll read that whole thread too.

    I totally get what you say about worrying over a few thousand dollars down the road. You're right. But what also motivates me is that when I do decide to put it up for sale, I want it gone gone gone, without giving it away. Thanks Dave!

    Yeah, that's the thread. I read it, good thread. There wasn't anything definite about the X-15E minimum cruise rpm. I did gather that the X-15P(erformance) likes the rpm ... at least until it hits the governor at 1,700 rpm. It was stated the Efficiency will run lower rpm effectively versus the Performance. But how low ... not clear (at least to me).
     
  5. Dave1837

    Dave1837 Medium Load Member

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    I'm in an X15P currently. Can't run it below 1500 or it falls on its face. 18 speed with 3.36 rears and it's rare that I stay in 18th gear unless I'm running across Ohio. MPG is around 4.5-5.5 and I rarely ever idle it. Performance is mediocre, it will run good but you have to keep it wound up to 1800 on hills, makes peak HP at 1950.

    If you're looking for a low RPM engine the MX13 is probably your best bet. I loved the one I drove, made all its power between 1000-1400. I could run across I80 in PA and only drop it down into 17th once, rest of the time was 18th. It could get 6.5 mpg if I took it easy on it but I averaged 5
     
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  6. Bean Jr.

    Bean Jr. Road Train Member

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    Funny! N14 and 12.7 were opposite. You could pull an N14 way down, but let a 12.7 go below 1,400, it's done!
     
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  7. Dave_in_AZ

    Dave_in_AZ Road Train Member

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    I run my ISX between 1325 and 1450. Rarely break 1550 even on the big hills. DD15 is about the same.
    The one Vulva I had you had to wind up D13.

    I've never driven an X15, I kinda really wanted one too, until everyone started saying it was a high winder. I talked to a guy at Landstar at a shipper that had a brand new 680. He said it comes with 3 free parameter changes. He said the second one, whatever they tweak, made it run right. He said he was extremely disappointed when he first got it.
     
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  8. DUNE-T

    DUNE-T Road Train Member

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    What kind of freight are you hauling? The mpg seems to be very low on both trucks
     
  9. Dave1837

    Dave1837 Medium Load Member

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    Lumber, coils and trim board mainly, they all net about 46-48k every time. The hills around here don't help much either
     
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  10. Jax Graddy

    Jax Graddy Bobtail Member

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    I finally found some information. I would like to know if you drivers that are ACTUALLY driving an Efficiency will agree, or not agree.

    "The X15 Efficiency engine is geared for 1150 rpm at cruise speed..." says Tim Proctor, Cummins ‎Director, Engineering. In the below article.

    Cummins new X15: Every little bit helps—a lot | American Trucker
     
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